This invention relates to the dispersion of cellulose esters in elastomers as small particles to improve the mechanical and physical properties of the elastomer. Polar cellulose esters (CE) are incompatible with non-polar elastomers. In addition, high melting cellulose esters do not melt at typical melt processing temperature of elastomers. These factors make dispersion of cellulose esters into elastomers difficult via most industrially utilized melt mixing process. Due to the above problems, cellulose esters are not an obvious choice as an additive to non-polar elastomers.
This invention can overcome these difficulties by using plasticizers where necessary to help reduce the melt temperature of cellulose esters and by using compatibilizers to help improve mixing and compatibility of cellulose esters and elastomers. Although not wishing to be bound by theory, it is believed that the compatibilizers used can also improve mechanical and physical properties of the cellulose ester/elastomer compositions by improving the interfacial interaction/bonding between the cellulose ester and the elastomer. These cellulose ester/elastomer compositions can be used in rubber/elastomeric applications ranging from tires, hoses, belts, gaskets, automotive parts, and the like.
A process of dispersing cellulose esters in elastomers involves melting or softening cellulose esters so that the cellulose esters can flow and subsequently break down into small particles (dispersion) under shear processing. After dispersion, the cellulose esters can re-solidify upon cooling to room temperature to reinforce the rubber. Therefore, the incorporation of cellulose ester into elastomeric compositions can lower Mooney viscosity which can help with the processing of the composition through equipment, such as, mixers, calenders, extruders, and molding equipment. It can also provide longer scorch safety which provides for a longer safety time during processing. Shorter cure times can also be obtained which allows for faster turnaround time in curing molds and presses. The addition of the cellulose ester to the elastomer can also provide for higher break stress/strain, higher low strain modulus, and higher tear strength providing a tougher and stiffer composition. Finally, the addition of the cellulose ester can provide a lower tan delta at 30 C which allows for lower heat buildup and lower hysteresis.